The present invention relates to an apparatus and a method of investigating surfaces, and in particular coatings. The invention is described with reference to so-called effect coatings, i.e. those coatings which have so-called effect pigments. Effect pigments of this type cause the coating in question to shine or sparkle or to assume a specific colour under specified conditions, for example with a light arriving at a specified angle.
In this case the most widely varying effect pigments and also the most widely varying optical properties thereof are known from the prior art. In this way, these effect pigments can have for example the most widely varying changes of colour.
Measurement instruments or apparatus are known from the prior art which are also used for the colour detection or optical detection of coatings of this type. In this case these apparatus usually have a plurality of light sources which direct specified light, for example standardized white light at different angles onto the respective surface provided with the coating. The radiation reflected by this surface is recorded by a camera, such as for example a CCD colour camera and the images are evaluated accordingly.
In this case, however, on account of the system there are limits to the accuracy of measurements of this type. Colour-image cameras of this type usually have an array with a plurality of photo detectors, in which case those detectors which are used to detect red light components, the detectors which are used to detect green light components and the detectors which are used to detect blue light components in each case are additionally arranged in any case at slightly different positions.
If coatings of this type with effect pigments are now recorded by a suitable appliance it is possible, in the event that an effect pigment reflects light in the red colour range for example, for this light to be reflected under specified measurements to those photocells which are intended to record blue or green light. In this case the corresponding photocells will display relatively low values or intensities and, in this way, the result is falsified.
In addition, in the case of illumination with a plurality of radiation sources of different spectral composition the separate illumination sources can be supplied with current individually. As a result, the brightness of this illumination can be adapted to the sample or the sensor characteristic for example in an optimum manner, and so a maximum measurement dynamic is achieved for each illumination.
The object of the present invention is therefore to provide an apparatus and a method which will permit a more accurate recording, or a less falsified recording, in particular of coatings with effect pigments.